5 Common FAIA Validation Errors and How to Fix Them

FAIA validation can surface dozens of distinct error types, from minor formatting issues to critical problems that will cause the Luxembourg tax authority to reject your file. Based on common validation patterns, these five errors account for the majority of FAIA failures. For each one, we explain what it means in plain terms, why it happens, and what to do about it.

Regardless of which accounting software generates your FAIA files, understanding these errors will save you significant time during the validation and submission process.

Error 1: File Not Recognised as FAIA

Why It Happens

Every FAIA file must include a specific identifier that tells the tax authority’s systems which standard and version it follows. When this identifier is missing, misspelled, or set to an older version, the file cannot be validated at all. It is the equivalent of submitting a form without a title: the recipient does not know what they are looking at.

This typically happens when accounting software is configured for an older FAIA version, or when the export template was not properly set up for Luxembourg requirements.

How to Fix It

• •Ask your software vendor to confirm that your FAIA export is configured for version 2.01 with the correct OECD SAF-T identifier.
• •Check after software updates: Upgrades or patches to your accounting system can sometimes reset export settings. Verify the FAIA configuration after any update.

Error 2: Invalid TVA (VAT) Tax Codes

Why It Happens

Luxembourg uses a specific set of TVA (Taxe sur la Valeur Ajoutée) codes that differ from the generic VAT codes used in other countries. A common mistake is using codes like "VAT20", "STD", or "ZERO" which may be standard in UK or other European configurations but are not valid for Luxembourg FAIA files.

Each valid Luxembourg tax code follows the TVA- prefix convention and maps to a specific rate or exemption category.

How to Fix It

Make sure your accounting software maps its internal tax codes to the correct Luxembourg TVA codes when generating the FAIA export. The valid codes are:

• •Prevention: Create a tax code mapping between your accounting system’s internal codes and the Luxembourg TVA codes above. Review this mapping whenever you upgrade your software.

Error 3: Missing Master Data References

Why It Happens

A FAIA file must be self-contained: every account, customer, and supplier referenced in your invoices, journal entries, and payments must have a matching record in the master data section. This allows the tax authority to audit the file without needing to look anything up in your accounting system.

This error commonly occurs when the export covers a date range that includes transactions referencing master data created before the export period. It also happens when customer or supplier records have been deleted, merged, or archived in your accounting system after the transactions were recorded.

How to Fix It

• •Include all referenced records: Make sure your export includes master data entries for every customer, supplier, and account that appears in a transaction, even if the record was created outside the reporting period.
• •Check your chart of accounts: Every account used in journal entries must appear in the master data. This is the most frequently missed reference type.
• •Review customers and suppliers: Cross-check that every customer on a sales invoice and every supplier on a purchase invoice has a corresponding master data record.
• •Prevention: Ask your software vendor to confirm that the FAIA export builds the master data section from the actual transactions, rather than from a separate data extract. This prevents mismatches by design.

Error 4: Incorrect Decimal Precision

Why It Happens

Luxembourg FAIA rules expect tax rates and monetary values to include at least two decimal places. A tax rate written as "17" instead of "17.00" can trigger validation errors. The same applies to monetary amounts: "1250" should be "1250.00".

This often occurs when accounting software stores values as whole numbers internally and only adds decimal places for display. When the raw value is exported to the FAIA file, the decimal precision is lost.

How to Fix It

• •Prevention: Ask your IT team or software vendor to confirm that the FAIA export formats all monetary values and tax rates with at least two decimal places. Test with edge cases such as zero values and whole-number rates.

Error 5: Wrong Date Format

Why It Happens

All dates in a FAIA file must follow the international standard format: YYYY-MM-DD (e.g., 2025-03-15). This is a strict requirement. Any other format will cause the file to fail validation immediately.

The most common cause is accounting software configured for US date format (MM/DD/YYYY) or European display format (DD/MM/YYYY or DD.MM.YYYY) that exports dates without converting them. Database exports may also produce dates in different formats depending on regional settings.

How to Fix It

• •Prevention: Ask your IT team or software vendor to set the date format in the FAIA export to YYYY-MM-DD explicitly. Do not rely on regional system settings, as these can differ between environments.
• •Watch for mixed formats: Some date fields expect a date only, while others may include a time component. Check that your export handles both types correctly.

Summary: A Validation Checklist

Before submitting your FAIA file to the Luxembourg tax authority, run through this checklist to catch the most common issues. The FAIA Validator checks all of these automatically when you validate your file.